. Can. J. Chem. 55,3951 (1977).The thermal decarbonylation of 2,2-dimethyl-3-butenal is shown to be an intramolecular extrusion of carbon monoxide concerted with the transfer of hydrogen (deuterium) to the y-position. The reaction displays a kinetic isotope effect of 2.8 (at 296.9"C) and follows first order kinetics (E, = 44.2 L-0.2 kcal mol-l, log A = 13.4 k 0.3).ROBERT J. CRAWFORD, STUART LUTENER et HIROKAZU TOKUNAGA. Can. J. Chem. 55,3951 (1977).On dkmontre que la dkcarbonylation thermique du dimkthyl-2,2 buttne-3 a1 est une extrusion intramoltculaire de monoxyde de carbone concertke avec un transfert d'hydrogkne (deutkrium) vers la position y. La rtaction prtsente un effet isotopique cinttique de 2.8 (a 296.9"C) et suit une cinktique du premier ordre (E, = 44.2 + 0.2 kcal mol-', log A = 13.4 + 0.3).[Traduit par le journal] IntroductionRecently we examined the thermolysis of 2-vinyloxirane (1) and concluded that one of the initial products was 3-butenal which, depending upon the surface of the vessel, was tautomerized to E-or 2-2-butenal or produced propylene and carbon monoxide. Traces of oxygen brought about a catalytic reaction and large amounts of CO and propylene were produced, but even after the most careful conditioning propylene and CO were present. We suggested that the decarbonylation of 3-butenal was both radical catalyzed and under oxygen free conditions proceeding via an intramolecular mechanism. To study this more thoroughly we have examined the thermolysis of the non-enolizable 2,2-dimethyl-3-butenal (1). There are few instances of decarbonylation of P,y-unsaturated aldehydes. The most thoroughly studied is the work of Schaffner (2) where the singlet photosensitized decarbonylation of R-(+)-laurolenal (2) to S-(-)-1,2,3-trimethylcyclopentene (3) is observed.

. Can. J. Chem. (1974).The thermolysis of 4-methylene-1-pyrazoline and the kinetic isotope effects of 3,3-d,, 3,3,6,6-d4, and 3,3,5,5,6,6-d6 compoilnds were examined. Data suggest a simultaneous cleavage of both carbon-nitrogen bonds with the formation of an intermediate which by 13C labelling is shown to be other than the triplet planar trimethylenemethane. Product studies on 3,3-dimethyl-4-methylene-1-pyrazoline and 4-isoplopylidene-1-pyrazoline are best rationalized in terms of the Chesick type intermediate. (1974).La thermolyse de la methylene-4-pyrazoline-l et les effets isotopiques des composts 3,3-d2, 3,3,6,6-d4 et 3,3,5,5,6,6-d6 ont Ctt examines. Les resultats suggerent une rupture simultanee des deux liaisons carbone-azote avec formation d'un intermtdiaire qui, par marquage au 13C, s'averC &tre different du trimCthylenemethane plan a I'ttat triplet. Les produits de la dimethyl-3,3-methylene-4-pyrazoline-l et de l'isopropylidene-4-pyrazoline sont interprttes au mieux avec un intermediaire du type Chesick.

The 1Hmr and 13Cmr spectra for 15 4-alkylidene-1-pyrazolines and 19 alkylidenecyclopropanes are reported. The assignments of E and Z isomers are made on the basis of shielding effects about the exo cyclic double bonds. The addition of diazomethane-d2 to 1,2-butadiene is shown to be both regiospecific and stereospecific.

ROBERT J. CRAWFORD and HIROKAZU TOKUNAGA. Can. J. Chem. 52,4033 (1974). The thermolysis of 3,3,5,5-tetramethyl-4-methylene-1-pyrazolne (1) proceeds at 1/63 the rate of 4-methylene-1-pyrazoline. The activation parameters, log (kls-') = (15.53 f 0.3) -(40.7 f 0.4)/0 where 0 = 2.303 R T in kcal mol-', suggest that 1 is undergoing thermolysis by a mechanism different from that for 4-methylene-1-pyrazoline. The 2,2,3,3-tetramethylmethylenecyclopropane (5) produced rapidly isomerizes under the reaction conditions to 2,2-dimethylisopropylidenecyclopropane (4). The four opposed methyl groups of 5 have created sufficient ground state destabilization as to cause its isomerization to be 147 times faster than the conversion of 2,2-dimethylmethylenecyclopropane to isopropylidenecyclopropane.The products are considered in terms of two possible intermediates, one wherein an allylic diazenyl diradical is considered and the second wherein a Chesick type of intermediate is invoked. For the latter it is demonstrated that substituents on the orthogonal radical center can affect the rotational propensities of methylene GS. isopropylidene of the allylic system. ROBERT J. CRAWFORD et HIROKAZU TOKUNAGA. Can. J. Chem. 52,4033 (1974). La thermolyse de la tCtramCthy1-3,3,5,5-m6thylt.ne-4-pyrazoline-l (1) s'effectue avec une vitesse Bgale a 1/63 de la vitesse de dCcomposition de la methylene-4-pyrazoline-1. Les parametres d'activation, log (k/sxl) = (15.53 * 0.3) -(40.7 + 0.4)/0 ou 0 = 2.303 R T en kcal mol-', suggerent que 1 subit la thermolyse selon un mecanisme different de celui de la mithylene-4-pyrazoline-1. Le tetramethyl-2,2,3,3-mCthylenecyclopropane (5) produit, s'isomerise rapidement, dans les conditions de la reaction, pour donner le dimethyl-2,2-isopropylidenecyclopropane (4). Les quatre groupes mithyle opposes de (5) crtent une dCstabilisation de ]'&tat fondamental suffisante pour que son isomerisation soit 147 fois plus rapide que la conversion du dimethyl-2,2-methylenecyclopropane en isopropylid~necyclopropane.On considere les produits en faisant intervenir deux intermediaires possibles, l'un dans lequel un diradical allylique-diazenyl est considere et le second dans lequel un intermtdiaire du type Chesick est invoque. Pour ee dernier, il est demontre que les substituents sur le centre radicalaire orthogonal peuvent affecter la tendance a la rotation du groupe methylene par rapport au groupe isopropylidene du systeme allylique. IntroductionAs a consequence of our work on the thermolysis of 4-alkylidene-1-pyrazolines (1) we have carried out an investigation of the gas phase thermolysis of 3,3,5,5-tetramethyl-4-methylene-1-pyrazoline (1). This structure has the advantage that the tautomerism, which plagued our previous studies, is no longer possible. Our principal objectives in studying 1 were to compare the competition between the isopropylidene group and the methylene group, of the presumed intermediate 2a, with the same competition observed in 26, the implied intermediate in the thermolysis of 4-isopropylidene-1-pyrazoline ...

'The racemization of (+)-2,3-divinyloxirane is facile at lMa, log (k,/s-l) = (11.3 + 0.5) -(30.1 +_ 0.4)/0 where 0 = 2.303RT in kcal mol-'. A slower but competitive rearrangement yields racemic 2-vinyl-2,3-dihydrofuran. The mechanisms of these reactions are discussed in terms of electrocyclic processes.-- Can. J. Chem. 51, 3718 (1973)